The present invention relates to a novel liquid crystalline compound and a liquid crystal composition. In particular, the present invention relates to a compound having fluorine-substituted 1,4-phenylene groups, a liquid crystal composition containing such a compound, and a liquid crystal display element constituted from such a liquid crystal composition.
Display elements produced from liquid crystalline compounds have been used widely in displays for watches and clocks, electronic calculators, word processors, and the like. (The term xe2x80x9cliquid crystalline compoundxe2x80x9d0 used herein is a generic designation for compounds that exhibit a liquid crystal phase, as well as compounds that do not exhibit a liquid crystal phase but are useful as constituting components for liquid crystal compositions.) In recent years, TFT displays having characteristics such as high contrast and wide viewing angle have been actively studied.
For liquid crystal compositions for TFT displays, there are demanded such properties as a high voltage holding ratio which has a very small degree of temperature dependence, a low threshold voltage (Vth) which has a very small degree of temperature dependence, wide range of mesophase, excellent miscibility with other liquid crystal materials, and low viscosity. Further demanded are improved response speed and contrast when they are used as a constitutional component of liquid crystal components. For example, compositions having a high xcex94n or a low threshold voltage is useful for improving response speed.
Fluorine-substituted liquid crystalline compounds are suitable as components constituting liquid crystal compositions having such properties, and a large number of such compounds have been examined as described in (1) Japanese Patent Publication No. 63-13411, (2) Japanese Patent Publication No. 63-44132, (3) Japanese Patent Application Laid Open No. 2-233626, (4) Japanese-translated PCT Patent Application Laid-open No. 2-501311, (5) Japanese-translated PCT Patent Application Laid-open No. 3-500413, (6) Japanese-translated PCT Patent Application Laid-open No. 3-503771, (7) Japanese-translated PCT Patent Application Laid-open No. 3-504018, (8) Japanese Patent Application Laid Open No. 4-217930, (9) Japanese-translated PCT Patent Application Laid-open No. 4-501575, (10) Japanese-translated PCT-Patent Application Laid-open No. 5-502676, (11) Japanese-translated PCT Patent Application Laid-open No. 6-504032, and (12) EP 436089.
An object of the present invention is to provide a liquid crystalline compound having a high voltage holding ratio which has a very small degree of temperature dependence, a low threshold voltage which has a very small degree of temperature dependence, a high xcex94n, and excellent miscibility with other liquid crystal materials at low temperature; liquid crystal compositions produced from these compounds having especially improved response speed and contrast; and liquid crystal display elements constituted from such liquid crystal compositions. The present inventors found that the above object is achieved by substituted benzene derivatives represented by general formula (1), thus completing the present invention. 
where, R represents a straight chain or branched alkyl group having 1 to 20 carbon atoms, in which each of optional and nonadjacent methylene groups (xe2x80x94CH2xe2x80x94) may be substituted by an oxygen atom; X represents a halogen atom, xe2x80x94CF3, xe2x80x94CF2H, xe2x80x94CFH2, xe2x80x94OCF3 or xe2x80x94OCF2H; each of Z1 and Z2 independently represents xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94 or a covalent bond, but Z1 and Z2 are not covalent bonds simultaneously; each of Y1, Y2, Y3, Y4, Y5 and Y6 independently represents H or F, but at least one of Y1, Y2, Y3 and Y4 represents F; and,
1) when Z1=xe2x80x94(CH2)2xe2x80x94, Z2=a covalent bond, and
a) when Y1=F and Y2=Y3=Y4=H, Y5=F,
b) when Y3=F and Y1=Y2=Y4=H, Y5=Y6=F,
c) when Y1=Y2=F, Y3=Y4=H and X=F or xe2x80x94CF3, Y5=F,
d) when Y1=Y2=F, Y3=Y4=H and X=xe2x80x94CF2H, Y6=H,
e) when Y1=Y3=F and Y2=Y4=H, Y5=Y6=F or Y5=Y6=H,
f) when Y3=Y4=F, Y1=Y2=H and X=xe2x80x94OCF3 or xe2x80x94OCF2H, Y5=F,
g) when Y3=Y4=F, 1=Y2=H and X=xe2x80x94CF3 or xe2x80x94CF2H, Y5=Y6=F,
h) when Y1=Y2=Y3=F, Y4=H and X=F, xe2x80x94OCF3, xe2x80x94OCF2H, xe2x80x94CF3 or xe2x80x94CF2H, Y6=H,
i) when Y1=Y2=Y3=F, Y4=H and X=Cl, Y5=F,
j) when Y1=Y3=Y4=F, Y2=H and X=F, Y6=F,
k) when Y1=Y2=Y3=Y4=F and X=F, xe2x80x94OCF3, xe2x80x94OCF2H, xe2x80x94CF3 or xe2x80x94CF2H, Y6=H, and
l) when Y1=Y2=Y3=Y4=F and X=Cl, Y5=F,
2) when Z1=a covalent bond, Z2=xe2x80x94(CH2)2xe2x80x94, and
m) when Y1=F and Y2=Y3=Y4 H, Y5=F and Y6=H,
n) when Y3=F and Y1=Y2=Y4=H, Y5=Y6=F or Y5=Y6=H,
o) when Y1=Y3=F and Y2=Y4=H, Y5=Y6=F or Y5=Y6=H,
p) when Y3=Y4=F, Y1=Y2=H and X=F, Cl, xe2x80x94OCF3, xe2x80x94OCF2H or xe2x80x94CF2H, Y6=H,
q) when Y1=Y3=Y4=F and Y2=H, Y6=H,
r) when Y1=Y2=Y3=Y4=F, Y6=H,
with the proviso that when Z1=xe2x80x94(CH2)2xe2x80x94, Z2=a covalent bond, Y3=Y4=F and Y1=Y2=H, X is neither F nor Cl; when Z1 is a covalent bond, Z2 is xe2x80x94(CH2)2xe2x80x94, Y1=F and Y2=Y3=Y4 H, X is neither F, Cl nor CF3; and any atom constituting this compound may be substituted by an isomer thereof.
Although some of the compounds represented by general formula (1) disclosed herein are included only perfunctorily in the above references (6) through (12) and other references, these references provide neither data on the compounds of the present invention nor specific descriptions of properties thereof, nor do they suggest the present invention.
Compounds represented by general formula (1) are classified into the following (a-1) through (a-32), and (b-1) through (b-32):
In these formulas, R has the same meaning as described above; B represents a 1,4-phenylene group; B(F) represents a 3-fluoro-1,4-phenylene group; B(F,F) represents a 3,5-difluoro-1,4-phenylene group; and Q represents the group shown below. 
Where Y5, Y6, and X have the same meanings as described above.
Although compounds represented by the above formulas (a-1) through (a-32), and (b-1) through (b-32) are all preferred, compounds represented by formulas (a-1) through (a-8), (a-17) through (a-24), (b-1) through (b-8), and (b--17) through (b-24) are particularly preferred.
In these formulas, R represents a straight-chain or branched alkyl group having 1 to 20 carbon atoms specifically exemplified by methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, decyl, pentadecyl, and icosyl groups as a straight-chain alkyl group; and isopropyl, sec-butyl, tert-butyl, 2-methyl-butyl, isopentyl, isohexyl, 3-ethyloctyl, 3,8-dimethyltetradecyl, and 5-ethyl-5-methylnonadecyl groups as a branched alkyl group. The branched alkyl group may be the one having optical activity, and such a group is useful as a chiral doping agent.
Each of optional, nonadjacent methylene groups may be substituted by an oxygen atom, specifically exemplified by an alkoxyl group such as methoxy, ethoxy, propoxy, butoxy, pentyloxy, and nonyloxy groups; and an alkoxyalkyl group such as methoxymethyl, methoxyethyl, methoxypropyl, methoxybutyl, methoxypentyl, methoxyoctyl, ethoxymethyl, ethoxyethyl, ethoxypropyl, ethoxyhexyl, propoxymethyl, propoxyethyl, propoxypropyl, propoxypentyl, butoxymethyl, butoxyethyl, butoxybutyl, pentyloxymethyl, pentyloxybutyl, hexyloxymethyl, hexyloxyethyl, hexyloxypropyl, heptyloxymethyl, and octyloxymethyl groups.
In general formula (1), each of Z1 and Z2 independently represents xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, or a covalent bond, and preferably, one of Z1 and Z2 is a covalent bond, and more preferably, one of Z1 and Z2 is a covalent bond and the other is xe2x80x94(CH2)2xe2x80x94, xe2x80x94CH2Oxe2x80x94, or xe2x80x94OCH2xe2x80x94.
Any atom constituting the compound represented by formula (1) may be substituted by an isomer thereof.
By suitable selection of these substituents or bonding groups, a compound having desired properties can be obtained.
A liquid crystalline compound according to the present invention represented by general formula (1) can be produced through commonly employed organic synthesis methods. For example, such a compound can be produced easily by the following method: 
where R, X, Y1 to Y6, and Z1 have the same meanings as described above; each of Xa and Xb represents a halogen atom; and m represents 1 or 2.
As is shown in Scheme 1, compound (1) of the present invention can be produced by allowing a halogen compound (4) to react with a dihydroxyborane derivative (5) in a mixed solvent containing toluene or xylene, an alcohol such as ethanol, and water, in the presence of a base such as K2CO3 or Na2CO3 and a catalyst such as palladium supported by graphite carbon (Pdxe2x80x94C), Pd(PPh3)4, or PdCl2(PPh3)2. Alternatively, as Scheme 2 shows, compound (1) of the present invention can be produced by allowing a halogen compound (4) to react with a lithium compound such as n-BuLi and a zinc compound such as ZnCl2 or ZnBr2, and then with a halogen compound (6).
As Scheme 3 shows, the compound (2) of the present invention can be produced by allowing a halogen compound (7) to react with lithium, then with a zinc compound and a halogen compound (6).
Also, as Scheme 4 shows, the compound (3) of the present invention can be produced by allowing a halogen compound (8) to react with a phenol derivative (9) in a solvent such as dimethyl sulphoxide, dimethyl formamide (DMF), 1,2-dimethoxyethane, tetrahydrofuran, hexamethylphosphorous triamide, or toluene, in the presence of a base such as sodium amide (J. B. Wright, et al., Journal of the American Chemical Society, 70, 3098(1948)), potassium carbonate (W. T. Olson, et al., Journal of the American Chemical Society, 69, 2451(1947)), triethyl amine (R. L. Merker, et al., the Journal of Organic Chemistry, 26, 5180(1961)), sodium hydroxide (C. Wilkins, Synthesis, 1973, 156), potassium hydroxide (J. Rebek, et al., the Journal of Organic Chemistry, 44, 1485(1979)), barium hydroxide (Kawabe, et al., the Journal of Organic Chemistry, 37, 4210(1972)), or sodium hydride (C. J. Stark, Tetrahedron Letters, 22, 2089, (1981), and K. Takai, et al., Tetrahedron Letters, 21, 1657, (1980)).
In general formula (1), a compound containing xe2x80x94Oxe2x80x94 in R can also be produced by similar methods.
The substituent X can be easily introduced by use of a previously introduced material, or through a well-known reaction at any process stage. Specific examples are shown below. In the formulas, Rx represents the following group: 
where R, Y1 to Y4, Z1, and Z2 have the same meanings as described above. 
where Y5 and Y6 have the same meanings as described above.
As Scheme 5 shows, a trifluoromethyl compound (10) can be produced by allowing compound (8) to react with a lithium compound such as n-butyl lithium and iodine to form compound (9), and allowing compound (9) to react with sodium trifluoroacetate/copper(I) iodide (G. E. Carr, et al., Journal of the Chemical Society Parkin Transactions I, 921, (1988)), or methyl fluorosulfonyl difluoroacetate/copper(I) iodide (Q. Y. Chen, et al., Journal of the Chemical Society Chemical Communications, 705 (1989)).
As Scheme 6 shows, a difluoromethyl compound (12) can be produced by allowing compound (8) to react with a lithium compound such as n-butyl lithium and a formylating agent such as N-formyl piperidine (G. A. Olah, et al., Angewandte Chemie International Edition in English, 20, 878(1981)), N-formyl morpholine (G. A. Olah, et al., the Journal of Organic Chemistry, 49, 385(1984)), or DMF (G. Boss, et al., Chemische Berichte, 1199(1989)) to form compound (11), and allowing compound (11) to react with a fluorinating agent such as diethylaminosulfur trifluoride (DAST) (W. J. Middleton, et al., the Journal of Organic Chemistry, 40, 574(1975); S. Rozen, et al., Tetrahedron Letters, 41, 111(1985); M.Hudlicky, Organic Reactions, 35, 513(1988); and P. A. Messina, et al., the Journal of Fluorine Chemistry, 42, 137(1989)), or morpholinosulfur trifluoride (K. C. Mange, et al., the Journal of Fluorine Chemistry, 43, 405(1989)).
As Scheme 7 shows, a monofluoromethyl compound (14) can be produced by reducing compound (11) with a reductant such as sodium borohydride (SBH), lithium aluminum hydride (LAH), diisobutyl aluminum hydride (DIBAL), or sodium bis-(2-methoxyethoxy)-aluminum hydride (SBMEA) to form compound (13), and allowing compound (13) to react with a fluorinating agent such as DAST.
As Scheme 8 shows, a trifluoromethoxy compound (17) can be produced by converting compound (15) by use of the method of Albert, et al. (Synthetic Communications, 19, 547(1989)) to form compound (16), and fluorinating compound (16) through the method of Kuroboshi, et al. (Tetrahedron Letters, 33, 29, 4173(1992)).
As Scheme 9 shows, a difluoromethoxy compound (18) can be produced by fluorinating compound (15) in a chlorodifluoromethane/sodium hydroxide system (Japanese-translated PCT Patent Application Laid-open No. 3-500413). Alternatively, it can be produced by use of the method of Chen, et al. (the Journal of Fluorine Chemistry, 44, 433(1989).
Halogen compounds and dihydroxyborane derivatives used as the materials can be produced by general organic synthesis methods, such as the following schemes: 
Where, R, X, Xa, Y1, Y2, Y5, and Y6 have the same meanings as described above.
As Scheme 10 shows, a halogen compound (20) can be produced by allowing compound (19) to react with a lithium compound such as n-BuLi, and iodine or bromine.
Also, as Scheme 11 shows, a dihydroxyborane derivative (22) can be produced by allowing compound (21) to react with a Grignard reagent prepared from and magnesium and a borane derivative such as trimethoxyborane or triisopropyloxyborane, and hydrolyzing the reaction product with hydrochloric acid or the like.
The reactions described above are well known to the art, and, needless to say, other known reactions may also be used.
Liquid crystalline compounds of the present invention thus obtained have a high voltage holding ratio which has a very small degree of temperature dependence, a low threshold voltage which has a very small degree of temperature dependence, and a high xcex94n. In addition, these compounds are easily mixed with various liquid crystal materials, and have high solubility even at low temperature.
Also, the liquid crystalline compounds of the-present invention are physically and chemically stable under conditions where liquid crystal display elements are normally used, and are excellent materials for the components of nematic liquid crystal compositions.
The compounds of the present invention can also be suitably used as the components of liquid compositions for TN, STN, and TFT displays.
The liquid crystal composition of the present invention will be described in detail below. Preferably, the liquid crystal composition according to the present invention contains at least one of the compounds represented by general formula (1) in a quantity of 0.1 to 99.9% by weight.
Specifically, liquid crystal compositions provided by the present invention are produced by mixing the first component containing at least one of the compounds represented by general formula (1), with a compound selected from a group of compounds represented by the following general formulas (2) to (9), depending on the application of the liquid crystal composition. 
where, each of R4 and R5 independently represents an alkyl group having 1 to 10 carbon atoms in which each of optional and nonadjacent methylene groups may be substituted by an oxygen atom or xe2x80x94CHxe2x95x90CHxe2x80x94, and optional hydrogen atoms may be substituted by fluorine atoms; each of ring G, ring I and ring J independently represents trans-1,4-cyclohexylene, pyrimidine-2,5-diyl, or 1,4-phenylene in which hydrogen atoms may be substituted by fluorine atoms; each of Z7 and Z8 independently represents xe2x80x94Cxe2x95x90Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or a covalent bond. 
where, each of R2 and R3 independently represents an alkyl group having 1 to 10 carbon atoms in which each of optional and nonadjacent methylene groups may be substituted by an oxygen atom or xe2x80x94CHxe2x95x90CHxe2x80x94, and optional hydrogen atoms may be substituted by fluorine atoms; X2 represents a CN group or xe2x80x94Cxe2x89xa1Cxe2x80x94CN; ring D represents trans-1,4-cyclohexylene, 1,4-phenylene, 1,3-dioxane-2,5-diyl or pyrimidine-2,5-diyl; ring E represents trans-1,4-cyclohexylene, 1,4-phenylene in which hydrogen atoms may be substituted by fluorine atoms or pyrimidine-2,5-diyl; ring F represents trans-1,4-cyclohexylene or 1,4-phenylene; Z6 represents a 1,2-ethylene group, xe2x80x94COOxe2x80x94 or a covalent bond; each of L3, L4, and L5 independently represents a hydrogen atom or a fluorine atom; each of b, c and d independently represents 0 or 1. 
where, each of R4 and R5 independently represents an alkyl group having 1 to 10 carbon atoms in which each of optional and nonadjacent methylene groups may be substituted by an oxygen atom or xe2x80x94CHxe2x95x90CHxe2x80x94, and optional hydrogen atoms may be substituted by fluorine atoms; each of ring G, ring I and ring J independently represents trans-1,4-cyclohexylene, pyrimidine-2,5-diyl, or 1,4-phenylene in which hydrogen atoms may be substituted by fluorine atoms; each of Z7 and Z8 independently represents xe2x80x94Cxe2x95x90Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or a covalent bond.
Preferred examples of compounds represented by general formulas (2) to (4) used in the liquid crystal composition of the present invention are as follows: 
where, R1 and X1 have the same meanings as described above.
Compounds represented by general formulas (2) to (4) have positive dielectric anisotropys, excel in thermal and chemical stability, and are very useful for the preparation of liquid crystal compositions for TFT displays requiring high reliability; e.g., high voltage holding ratios and large resistivities.
In the preparation of liquid crystal compositions for TFT displays, the compounds represented by general formulas (2) to (4) can be used within the quantity range of 0.1 to 99.9% by weight, preferably 10 to 97% by weight, and more preferably 40 to 95% by weight. Compounds represented by general formulas (7) to (9) may further be contained for adjusting viscosity.
Although compounds represented by general formulas (2) to (4) can be used for preparing liquid crystal compositions for STN and TN displays, the total content of these compounds is preferably not more than 50% by weight.
Preferred examples of compounds represented by general formulas (5) and (6) used in the liquid crystal composition of the present invention are as follows: 
where, R2, R3, and X2 have the same meanings as described above.
Compounds represented by general formulas (5) and (6) have large, positive dielectric anisotropys, and are used for lowering the threshold voltages of the liquid crystal composition. These compounds are also used for expanding the nematic range by adjusting optical anisotropy or elevating transparency points. Furthermore, these compounds are also used for the improvement of steepness of the liquid crystal compositions for STN or TN displays.
Compounds represented by general formulas (5) to (6) are particularly useful for the preparation of liquid crystal compositions for STN or TN displays.
When the quantity of compounds represented by general formulas (5) to (6) used in a liquid crystal composition increases, the threshold voltage of the liquid crystal composition decreases, but its viscosity increases. Therefore, so long as the viscosity of the liquid crystal composition satisfies the requirements, use of a greater quantity of the compounds is advantageous, because the displays can be driven at a lower voltage. In the preparation of liquid crystal compositions for STN or TN displays, the compounds represented by general formulas (5) and (6) can be used within the quantity range of 0.1 to 99.9% by weight, preferably 10 to 97% by weight, and more preferably 40 to 95% by weight.
Preferred examples of compounds represented by general formulas (7) to (9) used in the liquid crystal composition of the present invention are as follows: 
where, R4 and R5 have the same meanings as described above.
Compounds represented by general formulas (7) to (9) have small absolute values of dielectric anisotropys, and are nearly neutral. Compounds represented by general formula (7) are mainly used for adjusting viscosity or optical anisotropy. Compounds represented by general formulas (8) and (9) are used for expanding the nematic range; for example, thorough elevating clearing points, or for adjusting optical anisotropy.
When the quantity of compounds represented by general formulas (7) to (9) used in a liquid crystal composition increases, the threshold voltage of the liquid crystal composition increases, but its viscosity decreases. Therefore, so long as the threshold voltage of the liquid crystal composition satisfies the above requirements, use of a larger quantity of the compounds is preferred. In the preparation of liquid crystal compositions for TFT displays, the total quantity of compounds represented by general formulas (7) to (9) is preferably 40% by weight or less, more preferably 35% by weight or less. In the preparation of liquid crystal compositions for STN or TN displays, the total quantity of the compounds is preferably 70% by weight or less, more preferably 60% by weight or less.
In the present invention, an optically active compound is normally added for adjusting required twist angle by inducing the spiral structure of the liquid crystal composition, and preventing reverse twist, except in particular cases such as liquid crystal compositions for OCB (optically compensated birefringence) mode. As optically active compounds of the present invention, optically active compounds well known to the art may be used, and preferred examples include the following optically active compounds. 
Normally, these optically active compounds are added to the liquid crystal composition of the present invention for adjusting the pitch of twist. The pitch of twist is preferably adjusted within a range of 40 to 200 xcexcm for liquid crystal compositions for TFT and TN mode displays, and within a range of 6 to 20 xcexcm for liquid crystal compositions for STN mode displays. For bistable TN mode displays, the pitch of twist is preferably adjusted within a range of 1.5 to 4 xcexcm. Two or more optically active compounds may be added for adjusting the temperature dependence of the pitch.
The liquid crystal compositions of the present invention are prepared by commonly used techniques. Typically, various components are dissolved with each other at high temperature.
The liquid crystal compositions of the present invention can also be used as the liquid crystal compositions for guest-host (GH) mode displays by addition of dichromatic colorants such as merocyanine, styryl, azo, azomethyne, azoxy, quinophthalone, anthraquinone, and tetrazine dyes. The liquid crystal compositions of the present invention can also be used as the liquid crystal compositions for NCAPs produced by encapsulating nematic liquid crystals in micro capsules, or polymer dispersion-type liquid crystal display (PDLCD) elements represented by polymer network liquid crystal display (PNLCD) elements in which a three-dimensional matrix is formed in liquid crystals. In addition, such compositions can also be used as liquid crystal compositions for birefringence control (ECB) mode or dynamic scattering (DS) mode displays.
Examples of liquid crystal compositions containing the compounds of the present invention include the following. Compounds in the examples and in embodiments described below are represented by abbreviations according to the rules shown below. Compound numbers are the same as those shown in embodiments described below. In examples and embodiments, xe2x80x9cpercentagexe2x80x9d means xe2x80x9cpercentage by weightxe2x80x9d unless otherwise specified.